Whether it’s drummers wanting to go solo or action heroes wanting to tackle more highbrow material, it’s usually best to stick with what you know.

Video game spin-offs often come a cropper in the same way, with any divergence from a much loved formula alienating fans and underwhelming newcomers. Knight's Rush is different, in that it’s an even better game than the one that spawned it.

Knight’s tale

Abandoning the castle defence formula tackled by its predecessor and aligning with classic side-scrolling beat-‘em-ups, Knight's Rush is a matter of guiding your knight onwards, fighting through hordes of enemy knights, creatures, and defenses.

Developer MoreGames freshens the formula up, though, with a number of recognisably modern elements.

In the main Campaign mode you begin each level by selecting one of three knights, each with their own strengths and unique abilities. There’s a big, butch dark knight, who wields a giant hammer; a nimble green knight with two scythe-like blades; and a traditional grey knight with a sword and shield.

While there are a few minor differences between these warriors from the start, the real differences manifest themselves as you gain experience and level up.Squire in training

Entering the abilities menu by tapping the top-left corner of the screen, you can then assign the points you’ve accrued to a number of skills and perks.

Skills relate to your knight’s general abilities, such as special or magical attacks (which recharge over time), or simply the level of speed or strength with which they move and attack.

Perks, meanwhile, enhance the way in which your basic actions work. For example, you might be able to assign points to allow for double jumps or for your basic attack to occasionally unleash a fireball.

The interesting thing is that the available options differ slightly with each character. For instance, the green knight possesses the unique ability to buy a large chunk of health, whereas the black knight can be granted the nifty ability to cause damage when he lands after a jump.

MoreGames the Brave

By the end of each strikingly different world – which consist of three or four subtly different sections, adding up to 30-60 minutes of gameplay – you emerge with a potent one-man army, capable of dishing out devastating magical attacks to the towering end-of-level boss.

Then, in an unsettling twist, you find yourself stripped of all your hard-earned powers for the next level. It’s quite a brave move from the developer, as it goes against the fundamental desire for reward through progression and growth, and I can see it rubbing some the wrong way.

But it’s a good idea, particularly for a portable game. It means that you get to progress your character to a potent stage within a short period of time - there’s no tedious grind. It also means that you get to experiment with the characters, rather than sticking with the one that you’ve levelled up the most.

Not that playing through Knight's Rush could ever be labelled a grind. The graphics are an incentive to progress in themselves, with a stunning cartoon-fantasy art style and chunky, detailed sprites.

Despite such detail, the game never misses a beat - even on my humble second-generation iPod touch. The action is slick and fluid throughout, despite the inevitable reliance on virtual controls.

Advance temporarily halted

There are issues that take a little of the sheen off Knight's Rush. The upgrade menu is mystifyingly clunky and tricky to use, returning you to the action every time you assign a single skill or perk point (you’re awarded several at a time).

Also, the game’s crying out for co-operative multiplayer. Every beat-‘em-up in history becomes more fun with a human companion (or two), so it feels like a missed opportunity. Perhaps another generous freebie is in order here, eh MoreGames?

While Knight's Rush would benefit from multiplayer, it doesn’t need it to enhance its value. It’s a seriously meaty game, with a lengthy Campaign mode and two excellent Endless modes.

It all adds up to a truly exceptional package, and one of the finest (not to mention best looking) action games on iPhone and iPod touch.